The mechanism of poliovirus RNA replication will be examined in this study. A soluble and template dependent form of a poliovirus-specific RNA dependent RNA polymerase will be used to study the synthesis of viral RNA in vitro. Specific objectives of this study are as follows. 1) Fully characterize the RNA product synthesized in vitro. Determine if the polymerase can synthesize complete copies of viral RNA in vitro. 2) Determine the template requirements of the polymerase and its specificity for poliovirus RNA. 3) Further analyze the primer requirement of the polymerase and determine if VPg (or its precursor) can act as a primer. 4) Complete additional studies on the polypeptide composition of the polymerase. 5) Further define the structure of the endogenous RNA replication complex.